Unable to send mail to Hotmail/MSN

I have a new 4.5.3NE install that is working great so far. I'm able to send & receive mail to/from almost anywhere. My problem is that my users can't send mail to hotmail.com and msn.com email addresses. I've found other problems that admins are having that are similar, but not quite the same. The messages don't go into the Junk folder, they don't show up at all. I've checked my logs, and even setup a debug_peer_list with hotmail.com in it. Everything looks good - I see the normal 250 messages, "Sender OK", and finally "status=sent". I thought it might have to do with reverse DNS not being configured, but I had my ISP take care of that a few days ago, and things still aren't working. Today I broke down and contacted M$ support, but they've been less than helpful, having me check filters, junk mail config, etc. on the hotmail side.

Has anyone experienced this? Any tips or pointers for things I can do?

Have you looked at the queue status in the admin UI? You can also look in the zimbra logs to see if the mail left your system, if it has then I don't know what to suggest other than it's a problem at the receiving end.

Sorry, I guess I should have been more clear. There's nothing in the queue, the mail goes out just fine, immediately. The more I investigate, the more it seems the problem is on the M$ side, but it's hard to get them to look at it - I'm still at the low level of support with those guys, so I'm wasting time adding addresses to my safe list, etc. etc.

OK, I see. I don't know much (well nothing really) about the service you're using, is there any logs with that or any whitelisting (I guess that's your safelist) facilities? Is it just mail from your Zimbra server that gets 'lost'? Are you on a private IP (i.e. a home user)? Do you have a reverse DNS? AOL is particularly bad at blocking those types of users. I can't send to any AOL account because my ISP doesn't supply 'professional' services even though I have correct DNS etc. etc... they decided that everyone is a spammer.

Just to see if I have the same problem, I can send you a test email from my zimbra server if you like?

I don't really know much about the Hotmail service either. I use it for IM, but never check my email there. I manage a ZCS Network Edition server, and one of my users notified me that he was unable to send to @msn.com or @hotmail.com accounts. I thought it might be the reverse DNS problem, but I took care of this over the weekend - had my ISP add the PTR record.

If you wouldn't mind, I'd like you to test from your server. I'll PM you my hotmail address.

Follow this instruction:
This will definitely happen if you have bad SPF records. If you've recently changed your email architecture, you might have forgotten that. Check out your domain at http://www.openspf.org/